Regulator for mechanical rectifier



Aug. 14, 1956 E. J. DIEBOLD 2,759,141

REGULATOR FOR MECHANICAL RRCTIFIRR Filed Jan. 15, 1953 5 Sheetfs-Sheet l IN VEN TOR.

A118 14, 1956 E. DIEBOLD 2,759,141

REGULATOR FOR MECHANICAL RECTIFIER Filed Jan. l5. 1953 5 Sheets-Sheet 2 Aug. 14, 1956 E. J. DIEBOLD 2,759,141

REGULATOR FOR MECHANICAL RECTIFIER Filed Jan, l5, 1953 5 Sheets-Sheet 5 INVENTOR.

Aug. 14, 1956 E. J. Dlt-:BOLD

REGULATOR `RoR MECHANICAL RECTIRIER 5 Sheets-Sheet 4 Filed Jan. l5, 1953 IE 4a www I M Irfan/545 Aug. 14, 1956 v E. J. D11-:BOLD 2,759,141

REGULATOR FOR MECHANICAL RECTIFIER Filed Jan. 15, 1953 5 Sheets-Sheet 5 Iz- E Ea- I United States Patent REGULATR FOR MECHANICAL RECTIFIVER Edward J. Diebold, Ardmore, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of'Pennsylvania Application January 15, 1953, Serial No. 331,467

15 Claims. (Cl. 321-48) My present invention relates to mechanical rectiiiers and more particularly it relates to a regulator for such rectiiiers.

As is well-known in the art, a mechanical rectifier produces D. C. current by making metallic contact between the proper phase of an A. C. system and an associated D. C. system during the time interval the particular A. C. phase is capable of delivering energy in the desired direction, then breaking the metallic contact when the A. C. phase reverses its potential in relation to the D. C. voltage.

Mechanically, the rectifier is a motor driven switch connecting the A. C. voltage to the load at such a time, repeatedly, and in synchronism with the A. C. frequency, that current ows continuously in one direction.

Mechanical rectiiiers are the most efficient rectiiiers known today since they present a resistance of the order of magnitude of a few milliohms in the desired direction and infinite resistance in the opposite direction.

The making and breaking operation in these rectiers must occur when the value of the currents at the time of making and of breaking is equal to zero so that the contacts are not in any way damaged. This problem was successfully overcome by the use of the commutating reactor in mechanical rectiers.

It was observed, in fact, that when a reactor of the saturable type was introduced in an A. C. system, .sufficient zero current time was provided for sparkless contact operation. This zero current time, commonly known as step, must be provided at the beginning and end of the conductive interval and the length of this step is' the period of time required for the core of the reactor to become magnetically resaturated.

It is well-known, in fact, that a commutating reactor will present practically infinite reactance when unsaturated and practically zero reactance when saturated. When a current flowing in a circuit provided with the unsaturate the commutating reactor. The now unsaturated commutating reactor presents such a high reactance that the current owing through the circuit remains at zero. It is during this time, as previously mentioned, that the making and breaking operation of the `contact is performed.

To summarize the above, the effect of the commutating reactor is to restrain current iiow while magnetization is making a complete reversal in either direction and to permit full current how the instant the core is saturated.

In a three-phase mechanical rectifier, the making operation of a second phase occurs before the breakingoper'- ation of the first phase to assure proper commutation. The time length in which both contacts are closed, in other words the time interval between the time when the contact of the Second phase is made and the time when the contact of the iirst phase is broken, is called overlap. For ideal commutation, the break f the first phase must occur in the middle of a step.

r[The D. C. output of the mechanical rectifier caribe .59 commutating reactor approaches the zero point, it will 2,759,141 Patented Aug. 14, 1956 ICC changed by delaying the point at which commutation takes place. This is usually accomplished by mechanically shift-ing the stator of the synchronous motor so that the contacts will close at a later point. The more the contacts are delayed the smaller will be the average A. C. voltage transferred to the D. C. side and, therefore, the lower the resultant D. C. output voltage. Shifting the stator of the synchronous -motor for varying the magnitude of the D. C. output voltage is performed by lwhat is commonly known as a regulator.

n ln addition to the previously mentioned regulator directly connected with the stator of the drive motor, an overlap control shaft or contact time shaft regulator -is needed. By this means, when the drive motor stator has been adjusted for high or low voltage, the contact overlap is made shorter or longer, respectively. For this adjustment, the overlap control shaft is raised or lowered with respect to the stationary contacts. The change of distance raises or lowers the mean level of the travel of the moving contacts and shortens or lengthens the time the contacts remain closed.

These regulators do not work correctly because the stator angle depends not only on the current but also on the overlap. The overlap and the contact time of the machine are also related in a rather complex way so that `by neglecting these relationships, the performance of the regulators becomes inaccurate or oscillatory.

My present invention overcomes the above-mentioned problems and consists essentially of what may be called an analogue computer which determines instantly the correct stator angle and overlap angle of a mechanical rectifier from the information furnished by the current regulator and the overlap regulator.

The main object of my present invention is, therefore, 'a mechanical rectifier in which the stator angle and the overlap angle are individually controlled by a current or voltage regulator and by an overlap regulator in such a way as to render the operation of the two regulators independent.

Such a computer may be a mechanical linkage, as hereinafter described, or may be any other linkage, mechanical, hydraulic or electrical. Its function is that of relating the stator angle to the overlap time.

Accordingly, a more speciiic object of the present 'invention is a mechanical linkage to relate the stator angle and the overlap time of a mechanical rectifier to the different voltage or current conditions at which the rectifier is operating.

The provision of my novel mechanical linkage in a mechanical rectifier makes the current or voltage regulator independent from the overlap regulator, thus making possible the successful operation of the mechanical rectifier without any regulator, with only one of the two regulators or with both regulators at the same time without making any changes on the machine itself.

The provision of such mechanical linkage isy satisfactory even when the above-mentioned automatic regulators are replaced by hand control.

A further object of my present invention is, therefore, the provision of means whereby a mechanical rectifier may be provided with one automatic regulator, with two automatic regulators or may be controlled simply by hand.

My novel regulator consists, as previously mentioned, of a mechanical linkage operated by regulating vanes controlled by electrical quantities of the mechanical rectilier so that any particular change of these electrical quantities causes the correct angular displacement of the rotor of the driving motor with respect to the rotating lfield of the alternating voltage and the correct displacement of the overlap shaft.

Denoting by e, the angular rotation of one of these vanes and by y the angular rotation of the second vane, my novel mechanical linkage will transform these angular rotations into an angular displacement of the rotor of the driving motor with respect to the alternating voltage and displacement ,a of the contact time shaft so that correct operation of the regulator is achieved.

Another object of my present invention is the provision of an inexpensive, easy to manufacture regulating device for mechanical rectifiers.

These and other objects of my present invention will become apparent from the following description and drawings in which:

Figure 1 is a schematic diagram of a three-phase mechanical rectifier showing my novel current and voltage regulators.

Figure 2a is a plot with respect to time of the input and output voltage wave shapes for the three-phase mechanical rectifier of Figure l.

Figure 2b is a plot with respect to time of the current wave shape for the three-phase mechanical rectifier of Figure 1 showing the steps during which commutation can take place.

Figure 2c is a plot with respect to time of the closing times for the three pairs of contacts of the three-phase mechanical rectiier of Figure l.

Figure 2d is a plot with respect to time of the movement of one of the three pairs of contacts and their corresponding push rods.

Figure 2e is a plot with respect to time of the voltage across the winding of one of the commutating reactors.

Figure 2f is a plot with respect to time of the voltage across the input of the overlap regulator of the threephase mechanical rectifier of Figure 1.

Figure 3 is a schematic diagram of a portion of the mechanical rectifier of Figure 1 showing my novel analogue computer for transforming angular rotations of the current and voltage regulators vanes into inter-related displacements of the rotor of the contact operating motor and of the overlap shaft.

Figure 4a is a plot with respect to time of the input and output voltage wave shapes for the mechanical rectifier of Figure l at maximum D. C. output voltage.

Figure 4b is a plot with respect to time of an A. C. current wave shape of phase 2 for the mechanical rectifier of Figure 1 when operating at maximum D. C. output voltage. y

Figure 4c is a plot with respect to time of input and output voltage wave shapes for the mechanical rectifier of Figure 1 operating at its lowest D. C. output voltage.

Figure 4d is a plot with respect to time of the A. C. current wave shape of phase 2 for the mechanical rectier of Figure l when operating at the conditions shown in Figure 4c.

Figure 5 is a plot showing the hysteresis loop for a saturable core.

Figure 6a is a plot of voltages showing the point of commutation of an ideal rectifier.

Figure 6b is a plot against time of the movement of the contacts of the mechanical rectifier operating with a make delay angle of zero.

Figure 6c is a plot against time of the movement of the contacts of the mechanical rectifier operating with a make delay angle of 60.

The mechanical recter Referring first to Figure l showing a schematic diagram of a three-phase mechanical rectifier incorporating my novel regulator, the mechanical rectifier 10 is shown connected to a three-phase transformer 11 which in its turn is connected to polyphase supply 12. In the present embodiment of my novel invention, I have shown the primaries 13 of transformer 11 connected in A while the secondaries 15 are connected in Y. Itis to be understood 4 that any other suitable connection of the three-phase transformer 11 may be used with my novel mechanical rectifier.

The high side 16 of secondary windings 15 of transformer 11 are connected each to a commutating reactor coil 18 wound on the saturable cores 20. Considering the first phase A of rectifier 10, coil 18A on one side is connected to secondary 15A of transformer 11 and on the other side to stationary contacts 21 and 24.

Coil 18B of the second phase B is connected to stationary contacts 22 and 25 and coil 18C of the third phase C is connected to stationary contacts 23 and 26.

The secondaries 15 of transformer 11 are also connected to energize the driving motor 30 of rectifier 10. The driving motor 30 is a synchronous motor and its rotor operates movable contacts 31-32-33-34-35- 36 as hereinafter described.

The rectified electrical energy is supplied to a line consisting of conductors 39 and 40. To conductor 39 are connected stationary contacts 41, 42 and 43 while to conductor 40 are connected stationary contacts 44, 45 and 46.

The movable contacts 31-36 serve to bridge pairs of stationary contacts such as 21 and 41 whenever the desired portion of alternating voltage or current is to be applied to the D. C. line 39 and 4t). This is done automatically by synchronous motor 30 which by rotation of its shaft shown schematically at 50 moves the movable contacts 31 to 36 to bridge the stationary contacts such as 21 and 41 in the correct time relationship.

In the present embodiment, I have shown conductor 39 as the positive conductor of the D. C. transmission line 39-40 so that conductor 40 is the negative conductor.

The operation of this rectifier may be best understood by referring to Figure 1 in conjunction with Figures 2u, 2b and 2c. Figure 2a shows a plot of the three-phase voltage appearing at the secondaries 1S of transformer 11 and of the rectifier voltage appearing at the D. C. line 39-40.

More specifically, E1 is the wave shape of the voltage appearing across the secondary 15A of the first phase A. behind Ei is the wave shape of voltage Ez as it appears across the secondary 15B of phase B. Similarly, 120 behind E2 is E3 which is the voltage appearing across the secondary 15C of phase C.

It will be noted that in Figure 2a while the voltages E1, E2, and E3 representing the secondary voltages of transformer 11 are pure sine waves and are shown by solid lines, the voltage appearing as the D. C. line voltage is given by the vertical distance between the lines Ei, E2, E3 and E1', E2', E3' as indicated by the vertical shading. The cross hatched area represents the voltage loss due to commutation.

The D. C. voltage appearing across conductors 39 and 40 follows the transformer terminal voltage, for example E1, until commutation begins, that is, until contact 32 closes when Contact 31 is still closed. This is generally called the beginning of the commutation period. From this point on, the voltage across conductors 39-40 is kept at the average value of the two phase voltages E1 and E2 that are commutating, that is, phases A and B, and at the end of the commutating period suddenly jumps to the new transformer terminal voltage as can be seen at 57.

At 57 the commutation ends, that is, the full line current ows through contacts 22-32-42- The difference between voltages E1 and Ez, called commutating voltage, now appears on the commutating reactor coil 18A.

The exact time when a current reaches zero is dependent on the load current and the line voltage. lf the load current is small, the zero value would be reached earlier and when the load current is large, the zero value would be reached later in the cycle. To this it must be added that contacts 31 to 36 would be destroyed slowly if they had to interrupt more than a fraction of one ampere.

is due to' the fact that on a 60 cycle system, each contact 31 to 36must operate 216,000 times" an' hour.

The commutating reactors 20j 1hold the current through the contact at the point at which they would go through the zero point as described in application Serial No. 301,880, filed Iuly 31, 1952.

The effect of the commutating reactors 20 in the'circuits of the mechanical rectifier may be seen in Figure 2li where the currents I1, I2 and I3 are shownto stay at a small positive value at the point at which these currents would otherwise cross the zero point. A more detailed d escription of how the wave shapes of the currents I1, I2, andv I3 shown in Figure 2b areobtained from the sinusoidal voltages E1, E2 and `E3 'shown in' Figure 2a .may be found in the above-mentioned application.

Referring now to Figures l, 2a, 2b and 2c where 2c shows the closing intervals of the contacts 31 to 36 plotted against the same time scaleas' the `voltages E1, E2 and E3 and the currents I1, I2 and Ia, the time TA represents the time at which voltage E1 now decreasing becomes equal to the increasing voltage of the second'phase E2.' This is the earliest time at which a commutation from contact 31 to contact 32 can b'e started.

In other words, this is the earliest time at which 'contact 33, previously op'en as can be seen in Figure 2c, may now b'e closed while contact 31 stays closed.

At the time TA, the contacts 31 and 36 areclosed'as shown in' Figure 2c. The current I1 flows from the neutral point `of the secondary of transformer 11 through the winding A, coil 18A, contacts 21--3'1-41 into the positive line 39. The current Ia ows from' the' negative linel 40 through the contacts 46, 36, 26, the coil 13C and the winding 15C back to the transformer neutral. Hencev the currents I1 and I3 are equal to each' other as shown' in Figure 2b and are, in fact, identical with the D. C. output current of the mechanical rectifier. All the other contacts 32, 33, 34, 35 are open' at the time TA;

It will be assumed now that at a later time TB contact 32 is closed. Contact 31 still remains closed but now voltage E2 from the secondary winding 15B' of transformer 11 is higher than the voltage E1 of the secondary 15A of transformer 11. Current I2 rises while current I1 decreases because both voltages E2 and E1 are now s'hort-circuited ony the positive conductor 39 since movable contact 31 of phase A is bridging contacts 3141'while movable contact 32 of phase B is bridging the stationary contacts 42-32. As can be seen from curve 2`, of Figure' 2a, the D. C'. voltage wave shapeV follows the average value of E1 andEz resulting, therefore,in the curve shown at 57 of Figure 2a and an actual D. C.l voltage equal to E Ea (see Figure 4a).

At time TC, current I2 owing from secondary Winding 15B of transformer 11 to the positive conductor 39 through the movable contact 32 reaches the maximum value while I1 which flows from the secondary 15A of the transformer 11 to the positive conductor 39 kthrough contact 31 is now very nearly zero. At this point, core 20A of the commutating reactor of phase A because of the low value of the current I1 becomes unsaturated, thus increasing the reactance of coil 15A to a very llarge value (approximately 6000 times the total inductance of the circuitduring saturation). i

The short circuit voltage E1-E2'appears, therefore, its full value across coil 18A as can be seen from Figure 2e. The high reactance of coil 18A maintains current I1 at this very low value which, as previously mentioned, is carried by movable contact 31. At this time, contact 32 carries the fu'll current I2. From this time on, therefore, contact 31 can be opened without producing any damaging arc.

Overlp regulator Aroundsaturable core 20A is wound a second coil 60A so that when the core l20A of phase A has a high permeability due to its 4being unsaturated, the coils 18A and 60A of phase A become the windings of a transformer in which `coil 18A is the primary and coil 60A is the secondary'. l

Voltage E1-E2 which, as previously mentioned, appears across winding 18A` appears thus also across winding 60A. At this same time, the other two saturable cores 20B, 20C are both saturated because both Ig and I3, the current flowing in coils 18B and 18C of phases B and C, respectively, are at their peak values. Therefore', coils 18B and 18C present negligible reactance and their cores 20B and 20C present a very low permeability so that there is no transformer effect in phases B and C.

Connected between movable contact 31 and conductor 3.9'is a Winding 62A of transformer 63. Transformer 63 is provided with two more windings 64A` and 65A where winding-64 is connected between movable contact 34 and the negative conductor 40 and will, therefore, function in a manner similar to winding 62, while winding 65 is connected on one side to a parallel circuit67 consisting of two branches 68 and 69, each of which has crystal or dry cell rectiers.

More' specifically, rectiers 71 and 72 are in branch 68 and crystals 73 and 74 in branch 69 to forrn a bridge of which the four rectitiers 71 to 74 form the arms.

The mid point 76 between rectifiers 73 and 74 of branch 69 'is connected to a resistance 77 and the parallel combination of a capacitance 78 and a coil 80. Coil 80 is `the energizing winding of an electromagnet 81 having its armature 82 connected to arm 83 through spring 85. Arm 83 is pivoted at one end S6 on the frame 87. The other sidel of the parallel combination 78-80 is connected to the mid point between rectifiers 71 and 72 of branch 68. Armature 82 of magnet 81 is rigidly connected to a valve member 91 movable in channel 92.

The movable member 91 of valve 93 serves to control the How of alluid, for example oil, from the pump 95 through the pipe 96 into thechamber 97. Access of the fluid iny chamber 97 is possible through two channels 98 and 99, connecting chamber 97 with pipe 96 through valve member 91. The arrival of oil in chamber 97 causesay rotatable member 100 to rotate around its shaft 101.

At time TC (see Figures 2a to 2f), the secondary winding 62A is short circuited-by contact 31 so that the impedance of primary windings 65A is very very low. It is to be pointed out that the primary winding 65A is' connected in series to primary windings 65B and 65C of transformers 63B and 63C, respectively, of phases B and C.

Similarly, transformer 63B and 63C are short circuited, respectively, by contacts 32 and 36. Hence, the coils 60A, 60B and 60C connected in series with the primary windings 65A, 65B and 65C of transformer 63A, 63B and 63C have a totally induced voltage equal to Ei-Ez in the time interval TC to TD where TD is a time immediately after time TC when contact 31 opens to open the circuit between stationary contacts 2'1--41, thus interrupting the circuit of phase A of the mechanical `rectifier 10.

When contact 31 is in its open position, the winding 62A of transform-er 63A is opened and winding 64A which may be called the tertiary winding is also open so that primary winding 65A has now a very high impedance. Therefore, the voltage introduced in secondary 60A of transformer 18A-60A appears now across primary winding 65A and not any more across the parallel branches 65-7768L That is, voltage ERz now collapses as shown in Figure 2 which is a time plot of the voltage ER2 of the voltage regulator 110, comprising the main elements 100, 91, 81 and 67.

At' the next time TE, subsequent to TD, contact 31 should have opened; in other words, time TE is the limit of time during which the opening of contact 31 should occur. For safe operation, it is advisable to maintain TD approximately in the middle between TC and TE. TE coincides with TA for commutation of contacts 36 and 34 as may be sen from Figure 2c.

From the above, it can now be seen that the voltage pulses which constitute ERz (see Figure 2f) are proportional to the voltages of the phases which are in commutation. The beginning of these pulses coincides with the end of the actual commutation, namely TC, where TC is the beginning of the time interval during which contact 31 may be opened. The end of the pulse coincides with the opening of the contact in question, for example time TD.

As shown in Figure 1, the voltage ER2 is rectified by the system of rectiers 71, 72, 73 and 74 and is smoothened in the resistor 77 and capacitor 78. It can then be said that resistor 77 and capacitor 78 are the filters of the rectifying system 67.

A D. C. current IRz will then flow through the operating or energizing coil 80 of the regulator 110. Current IRz is proportional to the time elapsed between the beginning of the possible opening time of the contacts and the actual opening time of the contacts, in this case the contact being 31 and the time interval being the one between time TC and TD.

Since current TR2 is a function of the time interval between TC, when the step begins, and TD when the overlap ends, it may also be considered as a function of the overlap interval TB--TD and will, in fact, be described hereinafter as overlap time.

Energization of coil 80 by current IRz causes the attraction of armature 82 against the biasing force of spring 85. This will cause an upward movement in piston 91 of valve 93. Oil under pressure from pump 95 is then fed through pipe 96 and channel 98 into the upper half of vane 97 to turn shaft 101 in the counterclockwise direction. Shaft 101 in turn lowers the beam 83 which extends the spring 85 counteracting in part the action of the coil 80 upon the armature 82. This action of the beam 83 is commonly called an inverse feedback or a carry-back, a means to prevent hunting, as the output movement of the overlap regulator (shaft 101) counteracts the input movement of armature 82.

Decreasing the current IR2 will have the opposite effect as described above.

Current regulator In addition to overlap regulator 110, my novel mechanical rectiiier is also provided with what may be called a current regulator 120.

A current transformer 121 has its secondary 122 wound around conductor 16A of phase A of transformer 11.

A winding 124 connected in series to secondary 122 serves as the energizing winding of electromagnet 125. Armature 127 of magnet 125 is biased in this embodiment upwardly by a spring 128 secured at one end to armature 127 and at the other end to arm 130 pivoted at 131 on a frame 132.

Armature 127 is secured on its other side to a piston 135 of a valve 136. Piston 135 can move in a chamber 138 and controls the ow of fiuid from pump 95 to vane 140 by its motion in chamber 138.

Oil pumped from pump 95 fiows through pipe 141 into portion 142 of chamber 138 and thence, when piston 135 is in a certain position, in either channel 145 or 146 of vane 140, thus permitting a flow of oil into either the upper or lower chambers 147 and 148, respectively, of vane 140 causing the shaft 150 of rotatable member 151 to move either counterclockwise or clockwise.

More precisely, current IRi is taken from current transformer 121 to energize electromagnet 125. Energization of electromagnet 125 causes the attraction of armature 127 toward winding 124 against the biasing force of spring 128. Increasing the magnitude of current IRi causes the lowering of piston and a corresponding flow of oil from pump 95 into the lower chamber 148 of vane 140 and a consequent clockwise rotation of the movable member 151 and its associated shaft 150. The arm is operated by the vane shaft in such a way as to counteract the action of the current IRi upon armature 127 to provide an antihunting inverse feedback.

Analogue computer In the above description we have shown that under certain conditions of voltages and currents in my novel mechanical rectifier 10, a movable member 100 and 151 of the voltage and current regulator 110 and 120, respectively, will rotate in one or the other direction.

Referring now to Figure 3 showing a simplified schematic diagram of the mechanical linkages of my novel mechanical rectifier 10, it will there be seen that rotation of members 100 and 151 causes corresponding angular rotation of the stator 116 of synchronous motor 30 and a displacement p. in the overlap mechanism of the mechanical rectifier 10. In Figure 3 I have denoted by the same numerals the parts already shown in Figure 1 such as the contact structure and the movable members 100 and 151 of vanes 97 and 140, respectively. In Figure 3, in fact, A, B and C are the three alternating phases used in the mechanical rectifier 10.

In Figure 3 the movable contacts 31 to 36 are shown operated by a system of push rods 251-256. Push rods 251 and 254 form a pair connected to the ends of a common arm 261. Arm 261 is rotatable around a shaft 262 so that rotation of shaft 262 will cause contacts 31 and 34 to open or close the stationary contacts 21-41 and 24-44, respectively. Similarly, rods 252 and 255 are connected at the end of an arm 263 also mounted for rotation on shaft 262. Finally, push rods 253 and 256 are mounted at the end of arm 265 also mounted for rotation with shaft 262.

Arms 261, 263 and 265 are actually in this embodiment the horizontal leg of T-shaped elements 266, 267 and 268 having as vertical legs elements 271, 272, and 273. Members 271, 272 and 273 are pivoted on eccentrical arms 275, 276 and 277, respectively, which are moved by rotor 280 of synchronous motor 30 through shaft 50.

As previously mentioned, stator of synchronous motor 30 may be rotated by a certain angle, for example in order to produce a variation in the output D. C. voltage at conductors 39-40. This may be seen more clearly in Figure 4a, 4b, 4c and 4d.

Referring to Figure 4a showing the D. C. voltage delivered by the mechanical rectifier 10 when operating at the highest possible D. C. output voltage, it is there seen that this occurs when commutation starts exactly at time TA, that is, at the intersection of the decreasing voltage wave E1 and increasing voltage wave E2 so that at time TA, as mentioned, E1 and E2 have exactly the same value.

The cross hatched area 281 over the segment 57 represents voltage loss during commutation, that is, during the time in which both contacts 31 and 32 are in engagement with stationary contacts 21-41 and 22-42. This cross hatched area 281 starts at time TA and ends at time TC when the commutating reactor 18A-20A unsaturates.

The resulting current is shown in Figure 4b where I have denoted by aH the overlap interval, that is, the interval during which the two subsequently operating contacts are both in the closed position and by AtH the step length, namely, as previously defined, the period of time required for the core 20 to become resaturated.

When a larger phase difference L is introduced between synchronous motor 30 and the mechanical rectifier (by rotating the stator) such as shown in Figure 4c,

a smaller D. C. output voltage Eno is obtained from the niechanicalrectier since now the voltage loss consists of two parts: a shaded portion 281 due to loss in the commutation itself and area 282 which is a loss due to the delay in starting the commutation. Since now as seen in Figure 4c the effective D. C. voltage Enc is smaller than that obtained in the case of Figure 4a, the current of this phase, namely the second phase, plotted in Figure 4d, increases and decreases faster than it did intheprevious case and the step length At is also shorter than before.

To summarize the above, any rotation between the stator 160 and the rotor 280 of synchronous motor 30 from the optimum position H shown in Figure 4a produces a-decrease in the output D. C. voltage, but if the Contact overlap time ,MH is maintained as in Figure 4b, the current Iz will reverse before contact 32 opens and an arc will be established.

Therefore, unless the voltage control is limited to a small range it is necessary to vary the contact overlap time kto a new value ,aL smaller than MH. To vary the overlap time ,u it is necessary to provide a mechanical linkage 300' (see Figure 3) that while rotating by an angle the stator 260 with respect to the rotor 280 of motor 30 produces the correct change in overlap time.

This is accomplished by lowering the overlap shaft 262 through rotation of shaft 301 operating the eccentric member 302 which is pivoted on the arm 303 of the oscillating member 305. Member 305 may rotate at 306 when moved by shaft 301 through cam 302. Both displacement for motor 30 and ,4L/2 for the overlap shaft 262 where ,1L/2 determines the value of the overlap' angle n must be produced automaticaly by the change Vof the electrical quantities of mechanical rectifier 10. The eccentric fastened on shaft 301 operating member 302 and hence raising or lowering the overlap shaft 262 is of such a magnitude and angular position that the displacement of the arm 378 is the angle /L/ 2 when n is the angular expression for the overlap time (win- ',u). This is done in my novel regulator through vanes 97 and 140 of the voltage and current regulators 110 and 120, respectively.

As described above, the current IR1 and current IR2 cause the rotatable members 100 and 151 of vanes 97 and 140 to rotate by the make delay angle and overlap angle 'y, respectively, which through my novel mechanical linkage 300 produce the correct displacements ,B and ,a/ 2 for motor 30 and for overlap shaft 262, respectively.

Shaft 150 of rotatable member 151 of vane 140 is provided with two transverse arms 320 and 321 so that a rotation of shaft 150 will cause a similar rotation of arms 320 and 321. Arm 320 is provided in its turn with a longitudinal extension 323 engaging linkage 325 of computer 300. The coupling between longitudinal arm 323 of member 320 and linkage 325 is such that a rotation of shaft 150 and, therefore, of member 320 produces a longitudinal displacement of linkage 325.

More specifically, therefore, extension 323 of member 320 engages a cylindrical portion shown schematically at 326. Cylinder 326 is rigidly secured to linkage 325, while extension 323 of member 320 may rotate within cylinder 326. The second transverse member 321 rigidly secured to shaft 150 is also provided with a longitudinal extension 328 engaging 2 cylinders shown schematically at 329 and 330.

Extension 328 can freely rotate in the interior of cylinders 329 and 330. Cylinder 329 is n'gidlysecured at one end of linkage 332. The other end 335 of linkage 332 is shaped to obtain a slot 336. Similarly cylinder 330 is rigidly secured to linkage 337 which has at one end an extension 338 having a` slot 340. Slots 336 and 340 are engaged respectively by extensions 342 and 344 of member 345.

Extensions 342 and 344 are rigidly secured around a shaft 346- rotatable with respect to the portion 348 of the frame ofthe mechanical rectifier. A third transverse" extension 350 i's connected to shaft 346. A rotation of sha'ft 346 would therefore cause a similar angular ro'tation o'f extensions 342, 34'4 and 350. Similarly, a rotation of member 350 Will cause an angular displacement of shaft 346 and corresponding angular motion of ex# tension 342 and 344.

Member 350 is provided with a longitudinal extension 360 engaging a cylinder shown schematically at 361 secured to linkage 362. Extension 360 is freely rotatable in cylinder 361 and serves as coupling means so that an angular displacement of member 350 is transformed into longitudinal or axial motion of linkage 362. v

Linkage 362 is pivoted to linkage 363y at v364 while linkage 363 is pivoted at its other end at 365 to linkage 325'. Linkage 363 carries in intermediate position between pivots 364 and 365 a cylinder shown schemati-v cally at 366 which is engaged by extension 368' of shaft 101 of vane 97. Shaft 101 is actually provided with a transverse portion 367 to which extension 368 is also freely rotatable in the interior of cylinder 366.

Stator 160 of motor 30 is provided with a transversely extending arm 370 pivoted at 371 to a linkage 372. Link-v age 372 is pivoted at its other end 374 to the intermediate point of linkage 332; similarly shaft 301, the rotation of which controls the overlap interval n, is freely rotatable in bearings 375 and 376' andl is provided with a transverse arm 378 which is pivoted at its other end 379 to linkage 380. Linkage 380 is pivoted at its other end v3821 to an intermediate point of linkage 337.

It` isy now possible to describe the operation of my novel rectifier, assuming that because of voltage and current conditions in the mechanical rectifier 10, vane 97 has caused its shaft 101 to rotate counterclockwise by angular displacement y rand vane 140 has caused the shaft to rotate in the clockwise direction by an angular displacement a as previously described in connection with Figures l, 2, and 4.

These angular displacements 'y and a are transformed by my novel mechanical linkage or computer 300 into displacement and ,1L/2 of the stator 160 and the overlap shaft y262 according to the functions which govern commutation in mechanical rectiers.

To understand the' operation of my novel regulator, it will be assumed' rst that stator 160 and, therefore, arm 370 are rota-ted by an angle to delay the operation of th'e movable contacts 231 to 236 by the time /w where w is the angle frequency of the system. The movement of the pushrod 251 and of the movable contact 231 is plotted against time in Figure 2d and in Figure 6.

Figure 6 shows the movement of the three contacts 31, 32, 33 plotted against time. In Figure 6a there is no make delay (aL-"0) and no overlap (n=0); hence, the motor angle is also zero.

Figure 6a, therefore, corresponds to an ideal rectifier in which commutation takes place instantaneously at the time of equality of the phase voltages (E1=E2). Only an ideal rectifier will ever operate at a motor angle ,B equal zero.-

Fi-gure 6b' shows the movement of the three contacts 31, 32, 33 against time for a rectifier operating with a make delay angle zero (same as Figures 4a and 4b) and a finite overlap angle pH. Hence the stator of the motor must be turned by the angle relativelyto the ideal case. i

'Figure 6c shows the movement of contacts 31, 32, 33 when the make delay angle a=60 and the overlap angle=pL. l In this case the stator of the motor must be turned bythe angle L=';tL/2+aL, relatively to the ideal caseof Figure 6u. A v

Figure 6 shows clearly `how the motor angle ,Sand the level of the overlap shaft 262 must be changed to' accomplish a certain make delay angle a and a certain overlap n.

It will be noted that the make delay angle a determines the output of the rectifier. This angle, however, does not appear materially on the rectifier itself, except with the computer described in the present invention.

The motor angle which is available at the rectifier is a function of the wanted make delay angle a and the wanted overlap n, namely =al-p./2.

By adequate design of the eccentric 302 and the lever arm 273 against the eccentrics on 50, with the linkage 275-271-261, the turning angle of 301 ,tt/2 can be made equal to one-half the overlap angle n, i. e., the electric eye can thus be materialized As previously mentioned, the overlap shaft 262 which carries the rocker arms 271, 272 and 273 is fastened to arm system 305 which rotates around member 306. System 305 is operated by the eccentric 302 fastened on shaft 301; turning shaft 301 counterclockwise will simultaneously lower the level of all the push rods 351 to 356 (see Figure 6).

Lowering the level of push rods 351 to 356 will increase the time during which the contact is closed as may be seen in Figure 6b and by simple comparison with Figure 6a. In Figure 2e time interval TU is the time during which two contacts, for example 231 and 232, are closed simultaneously. In other words, time interval TU corresponds to the time interval between times TB and TD shown in Figure 2a.

It is well-known in the art that the ratio of output to input voltages in rectifiers is proportional to cos a where a is the angle by which the closing point of the contacts has been delayed (make delay). This angle is shown in Figure 2b as a time interval TB-TA for the frequency w since a-:w (TB-TA). In order to maintain a constant current in the rectifier circuit by means of the regulator 120 (see Figure l) the vane 140 operating at arm 150 must rotate by the angle a. so that the output voltage of the rectifier may be suitably changed.

From Figure 6 is easily seen then that az--l-n/Z.

It is also known from the theory of rectifiers that cos acos (a-l-n) :27 where y depends on the frequency, load and voltage condition alone, independently of a.

The angle 'y should be proportional to the voltage time integral between the curves E2 and E1 in the time limits TB to TD. The rst part of this integral TB to TC is constant. The second part TC to TD is given by the current 1R2 in coil 80 as shown above. Therefore, the output shaft 101 of the regulator 110 should move by 'y.

Shaft 101 is connected to 36S such that its vertical displacement is proportional to fy. Member 320 is connected by means of linkage 325 to linkage 363 so that its vertical displacement is proportional to cos a. The opposite end of the linkage 363 will, therefore, move by cos tnt-27: cos (a-i-n).

Member 350 is connected to linkage 362 in such a manner that member 350 moves by an angular displacement of (a+/r). Member 320-321 having moved by the angular displacement u. and member 350-342-344 by the displacement (a-l-a) the center 374 of linkage 332 will move by the average displacement of (a-l-n/Z) which is equal to the motor angle On the other hand, the center 381 of linkage 337 will move by 1/2 It is to be pointed out that the above description did not take into consideration the fact that in practical constructions mechanical rectifiers are provided also with saturable core make coils in addition to the break coils.

It is know, in fact, that contact can be made between the D. C. load and the A. C. phase without any special precautions only when the rectifier operates at maximum or near maximum voltage, but if the rectifier is operating at reduced voltage (as described above and produced by what may be called delayed commutation), the contact is required to close against an appreciable voltage and consequent current.

In practice it is impossible to make contact over the full contact surface instantaneously and, therefore, an arc would be established. Such operation would destroy the contacts in a very short time.

To overcome this difficulty, a second commutating reactor properly premagnetized (or biased) is introduced in each phase of the mechanical rectifier in series with the coil of the break reactors. By this means a make step is created at the time when contact 32 (Figure l) is to be closed.

Therefore, although in the above description the make operation and, therefore, the make reactors were neither considered nor shown, it is to be understood that such make reactors are used in a practical construction.

Mathematical treatment of regulation in mechanical rectyers In the following description the make operation and coils will not be considered with the understanding that in a practical construction their presence is necessary.

The three voltages E1, Ez, E3 in Figure 2a may be expressed mathematically as follows:

Ei=E-f2 sin wt 12F-Evi sin (af-2m) E3=E\/i sin (awa/3f) in which E is the R. M. S. value of the alternating voltages and -%1r and -l-Z/avr represent the phase displacements of voltages E2 and E3 with respect to Ei taken as reference.

In the following we will consider the commutation of contacts 131 and 132, during which time contacts 131, 132 and 136 are closed and while contacts 133, 134 and 135 are open.

Referring to Figure 1, it will be noted that when contacts 31 and 32 are both closed, the secondaries 15A and 15B of transformer 11 are short circuited and the only impedances existing in their circuit are those of coils 18A, 18B and those of series inductances 19A and 19B.

Letting lbf-:N952 where ,b1 and p2 are the total ux linkages of coils 18A and 18B, respectively, and qbl, 11, are the fluxes for one turn for coils `18A and 18B, we can write during the commutation time, that is, during time interval TB-TD this being the integral of the voltage equation of the commutation circuit during commutation time.

It will be noted that I1, I2 and I3 represent, respectively, the currents flowing in phases A, B and C of mechanical rectifier 10 following the convention used in Figure l.

In the above integral we have denoted by L the inductance of each coil 19 while the second subscript in the current and flux expressions represent the limit of integration.

In the above equation El-L Furthermore, referring to Figure 5 showing the hys- 13 teresis loop for the saturable cores 20, it will be noted that P1,D=N AB1,D 2,D=NAB2,D BLBZNABi l/zzNA-Ba It is also necessary to point out that the subscripts for flux density B shown in Figure denote the following operations: TB=make point TL=beginning of break step TC='beginning of llat part of break step TD=break point (variable) TN=end of at part of break step TE=end of break step If we now put Bc-B1v=AB and:

T wNAABU BD-BN E@ B c -B N where v=step length in radians (minimum) a--residual step, per unit value N =no. of turns of coils 18A, 18B, 18C

A =iron area E=R. M. S. alternating current voltage ER=rated voltage wR=rated frequency radians/sec.

tur-actual frequency I =direct current I R=rated direct current Z :network impedance as measured from the input (rated values) Z=ERV 11a/2 L=sum of air inductanees per phase ll=czz=per unit inductance per phase The above integrated voltage equation can be developed into Intrinsic (K=1.10 practically) K=constant a=0 break at trailing end of step o=l break at beginning of step 6:1/2 ideal break to be attained by regulation Equation 1 expresses and u as a function of fy which depends on the variables E, I, w and a. a 4as previously defined represents the make angle equal to w(T B-T A) while which may be called the mechanical overlap angle is equal to MTD-TB).

Equation 1 may be written in simplified form as follows;

where K1,Kz=Xed parameters, depending on design w, E, I=variables with unknown behavior For ideal commutation, a must be equal to l-a, that is, a must be equal to 1/2. This is equivalent to saying 14 that the break point, namely TD, must occur in the middle of the step TE-TC.

The overlap regulator 300 (see Figure 3) must make the value of 'y such that l-fr is equal to 1/2 for any value of w, E, I.

This is possible by adjusting the make angle and the mechanical overlap angle ,u such as to satisfy the equation:

cos 0:- cos (ot-ley.) =2fy this equation being solved `in the present regulator by the mechanical linkage 300.

ln order to determine the actual value of fy, the value of a or (l-a) must be measured, From the circuit shown in Figure l and the wave shapes shown in Figures 2e and 2f, it follows that the input current Inz` into the regulator Il() is (after rectification and integration by the circuits 67, 77 and 78 of Figure l) TD TD di 1102 dll/3) .TR2-K4 TC ER2dt-K4L'C 't- Etdt dt This equation can be integrated and simplified as was done for Equation l, thus obtaining where In is a constant function of design parameters.

Therefore, regulator 110 compares the value of 1-o' against the pull of the calibrated spring of Figure 1. Any deviation of 1 0-from the desired value 1/2 will Iresult in a displacement of the rotating member with a consequent rotation of shaft 101. This shaft as shown in Figure 3 provides the mechanical linkage 300 with the value of ry according to @galerien-ff) Whenever w, E or I change, the value of la as measured by Ina also changes to readjust Fy through regulator and linkage 300 until the regulator 110 is again at rest.

Considering now the current regulator for the direct current appearing at the conduct-ors 39 and 40, the relation between the direct current I, the direct voltage En across conductor 39-40 and the variable resistance of the load R is where direct current I lshould be constant at all times. The direct volt-age En can be calculated by an integration similar to the one used in the voltage regulator obtaining as a result:

3 E w I ED \/6 ER{R cos a-w-RQ/aE-x +KET)} where:

ER=rated alternating current voltage (R. M. S.) E=actual alternating current voltage (R. M. S.)

a=make angle This equation when solved for I gives E wf w1 I K5R cosa KR X7R where K5, K6 and K7 are constant parameters, E, R, I are unknown variables and a is determined by vane 147 of regulator 120. The function of this current regulator as previously mentioned is that of making the angle a so that the direct current I assumes the desired value for any E, R and w.

As previously described in connection with Figure l, current transformer 121 feeds a current Inl proportional to I into the measuring coil 124 of regulator 120. If I is not correct the regulator will turn the vane 147 and the shaft 150 (see also Figure 3) until current I returns to its correct value.

Arm 150 rotates, therefore, by a in a clockwise direction while linkage 350 moves in the counterclockwise direction by an angle et+/r. Link 37 is fastened to the arms 320 and 321 and 350 as previously described by portions of linkage 337 having the same length and lying in a horizontal plane so that the left-hand displacement of linkage 337 is a (in the downward direction) while the right-hand displacement is a+# in the upward direction.

The center point 381 of linkage 337 moves by the resultant displacement, that is, the average of a and -l-a-l-n which is equal to Therefore, member 380 pivoted on center point 381 of linkage 337 moves upwardly by and arm 378 rotates by wie in the clockwise direction.

It was earlier shown in connection with Figure 2e that the displacement angle of the stator 160 of drive motor 30 is given by When linkage 332 of my novel analogue moves by a in the downward direction at the left-hand end and by a-l-p, also in the downward direction at the right-hand end, its center 374 moves by the average of the two motions, that is,

Thus, member 37?. pivoted on center 374 of linkage 332 moves by in the downward direction and thus causes arm 370 connected to stator 160 of drive motor 30 to rotate by an angle in the clockwise direction, thus also moving stator 160 by the same angle It should be pointed out that in this description it was possible to substitute translational displacement, for

example, although is actually an angle in radiance since L* it is assumed that members such as 370 have unit length so that when they are rotated around one end by an angle they will cause a translational movement of the other end equal to ,8 itself.

l have described my novel mechanical rectifier 10 as being provided with one overlap regulator and one current regulator. However, it is easily seen that the current regulator can be replaced by a voltage regulator, a power regulator or any kind of other feasible regulator. The only change would consist in the particular connection of coil 124 to the voltage power or other electrical quantity of mechanical rectifier 10.

ln the foregoing I have described my invention solely in connection with specific illustrative embodiments thereof. Since many variations and modifications of my invention will now be obvious to those skilled in the art, I prefer to be bound not by the specific disclosures herein contained but only by the appended claims.

I claim:

l. In a polyphase mechanical rectifier for a polyphase circuit having means for increasing the zero current commutation time, regulating means comprising an analogue computer and consisting of mechanical linkages coupled to said rectifier, a current regulator coupled and responsive to the amplitude of the current in the said mechanical rectifier, an overlap regulator coupled to said circuit and responsive to overlap time, said current and overlap regulators being connected at their outputs to said analogue computer and causing said computer to maintain the output of said rectifier at a preselected value.

2. In a polyphase mechanical rectifier for a polyphase circuit having means for increasing the zero current commutation time, means coupled and responsive to the amplitude of the current in the said mechanical rectifier, means responsive to the magnitude of the overlap time, an analogue computer connected to and controlled at the outputs of said current and overlap responsive means and having an output connected to said rectifier for electromechanically controlling said rectifier to maintain the output of said rectifier at a preselected value.

3. lr. a polyphase mechanical rectifier for a polyphase circuit having means for increasing the zero current commutation time, means coupled and responsive to the amplitude of the current in the said mechanical rectier, means responsive to the magnitude of the overlap time, mechanical linkages operated simultaneously by said current and overlap responsive means and having an output connected to said rectifier for maintaining the output voltage of said rectifier at a preselected value irrespective of changes in the amplitude of the rectifier current.

4. In a polyphase mechanical rectifier for a polyphase circuit having means for increasing the zero current commutation time, a plurality of switches, said switches closing at a preselected direction of current flow, a motor having a stator and a rotor for operating said switches, means for varying the overlap intervals of said switches, means for regulating the output voltage of said rectifier, said regulating means comprising an analogue computer coupled to and controlled by electrical conditions in said circuit, said analogue computer transforming make delay angles and overlap angles into angular displacements of the stator of said motor with respect to its rotor and into variations in the overlap interval, said angular displacements of said stator and said overlap intervals being a preselected function of said make delay angles and overlap time.

5. In a polyphase mechanical rectifier for a polyphase circuit having saturable reactors in each circuit, switching means in each circuit for performing the rectifyiug operation and opening and closing during the time said saturable reactors are unsaturated, a mechanical analogue computer for regulating the output of said rectifier, transducing means coupled to one of said circuits and connected to said analogue computer for producing an angular motion which is a function of the amplitude of the current for operating said analogue computer, a second transducer means coupled to said one of said circuits and connected to said analogue computer for producing a second angular motion in said analogue cornputer which is a function of the overlap time of said switches, a synchronous motor having a stator and a rotor for operating said switches, said analogue computer being connected to said stator for varying the angle between the stator and rotor of said motor in response to the said two angular motions.

6. In a polyphase mechanical rectifier for a polyphase circuit having saturable reactors in each circuit, switching means in each circuit for performing the rectifying operation and opening and closing during the time said saturable reactors are unsaturated, a mechanical analogue computer for regulating the output of said rectifier, transducing means coupled to One of said circuits and connected to said analogue computer for producing an angular motion which is a function of the amplitude of the current for operating said analogue computer, a second transducer means coupled to said one of said circuits and connected to said analogue computer for producing a second angular motion in said analogue computer which is a function of the overlap time of said switches, a synchronous motor having a stator and a rotor for operating said switches and cam means for varying the overlap interval, said analogue computer being connected to said stator for varying the angle between the stator and rotor of said motor and said overlap intervals in response to the said two angular means.

7. In a polyphase mechanical rectifier for a polyphase circuit, means for regulating the output voltage, means responsive to load conditions coupled to said regulating means, said load responsive means comprising electrically controlled hydromechanical means.

8. In a polyphase mechanical rectifier for a polyphase circuit, means for regulating the output voltage, means coupled to said circuit and responsive to load conditions, the output of said last means being coupled to said regulating means, said load responsive means comprising a plurality of transducers, one of said transducers transforming a signal proportional to the amplitude of the load current into a signal utilizable by said regulating means, another transducer transforming a signal, which in a function of frequency, load and voltage conditions, into a signal also utilizable by said regulating means, and a connection from said regulating means to said rectifier for controlling said rectifier in accordance with said load responsive means.

9. In a polyphase mechanical rectifier for a polyphase circuit, means for regulating the output voltage, means coupled to said circuit and responsive to load conditions, the output of said last means being coupled to said regulating means, said load responsive means comprising a plurality of transducers, one of said transducers transforming a signal proportional to the amplitude of the load current into a signal utilizable by said regulating means, another transducer transforming a signal, which is a function of frequency, load and voltage conditions, into a signal also utilizable by said regulating means, and a connection from said regulating means to said rectifier for controlling said rectifier in accordance with said load responsive means, said regulating means comprising an electronic analogue computer.

10. In a polyphase mechanical rectifier for a polyphase circuit, means for regulating the output voltage, means connected to said circuit and responsive to load conditions coupled to said regulating means, said load responsive means comprising a plurality of transducers, one of said transducers transforming a signal in said circuit proportional to the amplitude of the load current into a signal utilizable by said regulating means, another transducer transforming a signal which is a function of frequency, load and voltage conditions, into a signal also utilizable by said regulating means, said regulating means comprising an electromechanical analogue computer and a connection from said electromechanical analogue computer to said rectifier for controlling said rectifier in accordance with the load and voltage conditions of said circuit.

11. In a polyphase mechanical rectifier for a polyphase circuit having means for increasing the zero current commutation time, said rectifier comprising a plurality of switches, a motor connected to and operating said switches to close contacts thereof at a preselected direction of current flow, means for varying the overlap intervals of said switches, means for regulating the output voltage of said rectifier, said regulating means comprising an analogue computer connected to and operated by said overlap varying means, said computer having an output connected to and operating said motor, said analogue computer transforming signals proportional to the voltage time integral of overlap into variations of the mechanical angle of said motor and corresponding variations of the mechanical overlap angle of the said overlap varying means so as to obtain the desired overlap integral.

12. In a polyphase mechanical rectifier for a polyphase circuit having saturable reactors in the path of the circuit, switching means in the circuit for performing the rectifying operation and openlng and closing during the time said saturable reactors are unsaturated, a mechanical analogue computer consisting of linkages for regulating the output of said rectifier, transducing means coupled to said circuit and responsive to electrical conditions in said circuit for applying on said analogue computer a movement which is a function of the time integral of the voltage during overlap, a synchronous motor having a rotor and a stator connected in the output of said computer for operating said switches and cam means in said last connection for varying the mechanical overlap angle, said analogue computer varying the angle between the stator and rotor of said motor and applying a movement to said cam means for varying the said mechanical overtap angle so as to obtain the desired overlap integral.

13. In a polyphase mechanical rectifier for a polyphase circuit having means for increasing the zero current commutation time, a plurality of switches in said circuit, said switches closing at a preselected direction of current fiow, a motor operating said switches, means for varying the overlap intervals of said switches, an overlap regulator connected in said circuit for producing signals which is a function of the voltage time integral at overlap, and an analogue computer, said analogue computer having linkages connected to the output of said overlap regulator and connected to said motor and transforming said signals into variations of the angle of said motor and of said mechanical overlap angle so as to obtain the desired overlap integral.

14. In a polyphase mechanical rectifier for a polyphase circuit having saturable reactors in the path of the currents, switching means for performing the rectifying operation and opening and closing during the time said saturable reactors are unsaturated, an output regulator in said circuit, an analogue computer connected to the output of said output regulator, a synchronous motor for operating said switches and cam means connected between said computer and switches for varying the overlap interval, said output regulator applying a signal to said analogue computer which is a function of the make angle, said analogue computer simultaneously varying the motor angle and the overlap angle to obtain the desired make angle.

15. In a polyphase mechanical rectier for a polyphase circuit having saturable reactors in the path of the currents, switching means for performing the rectifying operation and opening and closing during the time said saturable reactors are unsaturated, an output regulator in said circuit, an analogue computer connected to the output of said output regulator, a synchronous motor for operating said switches and cam means connected between said computer and switches for varying the overlap interval, said output regulator applying a signal to said analogue computer which is a function of the firing angle, said analogue computer simultaneously varying the motor angle and the overlap angle to obtain the desired tiring angle.

References Cited in the file of this patent UNITED STATES PATENTS 2,227,937 Koppelmann lan. 7, 1941 FOREIGN PATENTS 700,220 Germany Dec. 16, 1940 

